1. Field of the Invention
The embodiments discussed herein are related to a method of manufacturing a semiconductor device.
2. Description of the Related Art
Conventionally, in a semiconductor device (semiconductor apparatus) that uses (Si) semiconductor, a silicon carbide (SiC) semiconductor, etc., an ohmic contact (electrical contact portion) of a semiconductor portion and a transition metal layer (electrode) is formed by heat treatment (annealing). Here, a method of forming an ohmic contact in a conventional semiconductor device will be described taking an example where a nickel (Ni) contact electrode is formed on a silicon carbide semiconductor substrate (hereinafter, silicon carbide substrate).
FIG. 23 is a flowchart outlining a conventional method of manufacturing a semiconductor device. FIGS. 24, 25, 26, 27, and 28 are cross-sectional views of states of a conventional semiconductor device during manufacture. As depicted in FIG. 24, an interlayer insulating film 102 is formed in a front surface of a silicon carbide substrate 101. Next, a contact hole 103 is formed penetrating the interlayer insulating film 102 in a direction of depth, to reach the silicon carbide substrate 101 (step S101). Next, as depicted in FIG. 25, in the front surface of the silicon carbide substrate 101, a substantially 100% pure nickel layer (hereinafter, pure nickel layer) 104 is formed by a sputtering method, a vapor deposition method, etc. so as to be embedded in the contact hole 103 (step S102).
Next, as depicted in FIG. 26, by photolithography and etching, the pure nickel layer 104 is patterned and is left inside the contact hole 103 (step S103). Next, as depicted in FIG. 27, a pure nickel layer 105 is formed in a back surface of the silicon carbide substrate 101 by a sputtering method, a vapor deposition method, etc. (step S104). Next, as depicted in FIG. 28, by heat treatment at a temperature of 900 degrees C. or greater, the silicon carbide substrate 101 and the pure nickel layers 104, 105 are reacted to form a silicide layer 106 (step S105). Furnace annealing, laser annealing, lamp annealing, induction heating, etc. may be used for the heat treatment at step S105.
To form such an ohmic contact, a method has been proposed that includes a process of depositing a transition metal layer on a surface of a semiconductor substrate formed of a silicon semiconductor (hereinafter, silicon substrate) and a process of heat treating the transition metal layer, where in the heat treatment process, the entire silicon substrate is heated at a temperature of 400 to 750 degrees C. for 30 to 90 seconds (for example, refer to Japanese Laid-Open Patent Publication No. 2012-246216).
Another method has been proposed where a transition metal layer is vapor deposited on a contact on a silicon carbide substrate and the entire silicon carbide substrate is heated by rapid heat treatment at a temperature of 1000 degrees C. for 2 minutes to form a silicide electrode of high carbon content (for example, refer to Japanese Laid-Open Patent Publication No. 2009-177102 (paragraph 0017)).
Another method has been proposed where after a nickel layer is formed in a silicon wafer, hydrogen (H2) gas is introduced into a chamber to create a hydrogen gas atmosphere inside the chamber, and a susceptor is heated to 450 to 550 degrees C. to heat treat the silicon wafer (for example, refer to Japanese Laid-Open Patent Publication No. 2011-066060 (paragraphs 0037 to 0040)).
Still another method has been proposed where after a titanium (Ti) layer, an aluminum (Al) layer, and a silicon layer are sequentially formed on a silicon carbide substrate by sputtering to form a contact electrode, the titanium, aluminum, and silicon included in the contact electrode form an alloy with the silicon and the carbon included in the silicon carbide substrate by annealing using laser light (for example, refer to Japanese Laid-Open Patent Publication No. 2012-099599 (paragraphs 0042 to 0044)).
Yet another method has been proposed where an oxide film (SiO2), quantum dots formed from silicon, and a nickel (Ni) thin film are sequentially stacked on a silicon substrate and subject to remote hydrogen plasma processing for 5 minutes at a frequency of 60 MHz and a very high frequency (VHF) electrical power of 200 W to 500 W to form nickel silicide (NiSi) dots from a stacked film formed from the quantum dots and nickel thin film (for example, refer to Republished Japanese-Translation of PCT Application, Publication No. 2009-118783 (paragraphs 0056 to 0061) and K. Makihara, et al, “Self-Assembling Formation of Ni Nanodots on SiO2 Induced by Remote H2 Plasma Treatment and Their Electrical Charging Characteristics”, Japanese Journal of Applied Physics, Japan Society of Applied Physics, 2008.04, Vol. 47, No. 4, pp. 3099-3102).
Nonetheless, in Japanese Laid-Open Patent Publication Nos. 2012-246216, 2009-177102, and 2011-066060, the portion forming the ohmic contact (i.e., the transition metal layer, or the interface of the substrate and the transition metal layer) cannot be selectively heated; rather the entire substrate (the entire device) is uniformly heated. For example, when an ohmic contact of a silicon carbide semiconductor portion and a transition metal layer is formed, as described above, heat treatment at a high temperature of 1000 degrees C. or greater is performed. Therefore, interface properties of the semiconductor portion and gate insulating film, the material configuring the device, etc. may degrade. In Japanese Laid-Open Patent Publication No. 2012-099599, by reducing the spot diameter of the laser 105, a predetermined region can be selectively irradiated and therefore, the problems associated with Japanese Laid-Open Patent Publication Nos. 2012-246216, 2009-177102, and 2011-066060 can be resolved.
Nonetheless, with Japanese Laid-Open Patent Publication No. 2012-099599, the distance from the converging lens that converges the laser light, to the surface of the transition metal layer has to be constant across the entire transition metal layer. In other words, the device structure has to have a device surface that is flat without unevenness. Therefore, in cases where the distance from the converging lens to the surface of the transition metal layer is not constant consequent to the transition metal layer being disposed in a chip side wall or a trench side wall, throughput may decrease since laser irradiation has to be performed according to conditions corresponding to each irradiation position and therefore, not all of the transition metal layer can be simultaneously heated.
Further, with Japanese Laid-Open Patent Publication No. 2012-099599, since a predetermined region is selectively heated by laser irradiation, programming control for irradiation position, irradiation loci, etc. of the laser is complicated. Furthermore, irradiation voids occur consequent to deviation of the laser irradiation position, whereby contact resistivity becomes inconsistent; and near the transition metal layer, constituent portions (e.g., gate insulating film, etc.) other than the transition metal layer are heated, whereby device properties may degrade. Furthermore, if the surface area of the transition metal layer is smaller than the area corresponding to the spot diameter of the laser, a problem arises in that the transition metal layer cannot be selectively heated alone.
In Republished Japanese-Translation of PCT Application, Publication No. 2009-118783, since the transition metal layer alone generates heat by remote hydrogen plasma processing irrespective of device surface unevenness, transition metal layer patterns, etc., the transition metal layer alone can be uniformly heated. Therefore, problems occurring with selective heating of the transition metal layer by laser irradiation can be resolved. Nonetheless, in Republished Japanese-Translation of PCT Application, Publication No. 2009-118783 and K. Makihara, et al, “Self-Assembling Formation of Ni Nanodots on SiO2 Induced by Remote H2 Plasma Treatment and Their Electrical Charging Characteristics”, the mean free path of hydrogen atoms is large and high-density plasma is not created because the pressure is lowered to increase the lifetime of the hydrogen atoms. Therefore, a problem arises in that the hydrogen atom density becomes low and consequently rapid heating is not possible. In practice, in Republished Japanese-Translation of PCT Application, Publication No. 2009-118783, since plasma processing at a low electrical power of 200 W to 500 W is performed for a long period, during the plasma processing, constituent portions other than the transition metal layer (e.g., the entire device) are heated by a transfer of the heat generated by the transition metal layer and as a result, device properties may degrade.